To make a component which is exposed to extremely high temperatures, for example a heat shield element, such as a heat shield brick or a gas turbine blade or vane, able to withstand heat, it is known, for example from U.S. Pat. No. 4,321,311, to produce the component from a metallic base body and to coat the metallic base body with a ceramic thermal barrier coating of ZrO2. The ceramic thermal barrier coating is bonded in place by a metallic bonding layer made from an alloy of the MCrAlY type. Since the ceramic thermal barrier coating is generally a good conductor of oxygen ions, during operational use of the component, the bonding layer is partially oxidized, which can cause the thermal barrier coating to become detached from the metallic base body. Consequently, the duration of use of a component of this type is limited. This is the case in particular in the event of frequent temperature changes which occur when a gas turbine is being started up and stopped.
To improve the ability of piston heads to withstand temperature changes, the article “Keramische Gradientenwerkstoffe für Komponenten in Verbrennungsmotoren” [Ceramic gradient materials for components used in internal combustion engines] by W. Henning et al. in Metall, 46th Edition, Volume 5, May 1992, pages 436 to 439, has described a fiber ceramic body with a density gradient. This fiber ceramic body is composed of four layers of differing layer thickness with differing ceramic contents. The difference in the ceramic content consists in the ratio of fibers (Al2O3 short fibers) to ceramic particles of Al2TiO5 differing significantly in the four layers. Consequently, the porosity of the four layers also differs significantly from one another. The high porosity of the layers of between 40% and 79% is used to introduce molten metal into the voids in the fiber ceramic body by means of squeeze casting in order to produce a defect-free composite. In this way, it is possible to produce a piston head which has a metal and ceramic gradient which changes considerably and suddenly. The low thermal conductivity of the ceramic contents leads to the formation of a thermal barrier, thus insulating the piston. Moreover, the fiber ceramic mechanically reinforces the piston and thereby improves the ability of the piston to withstand thermal shocks.
The article “Projected Research on High Efficiency Energy Conversion Materials”, by M. Niino, M. Koizumi in FGM 94, Proceedings of the 3rd International Symposium on Functional Gradient Materials, ed. B. Ilschner, N. Cherradi, pp. 601-605, 1994 has described composite materials in relation to the development of materials for an orbital glider, and these materials are referred to as functional gradient materials (FGMs). A significant feature of FGMs is a continuous composition and/or microstructure gradient, which is intended to lead to a continuous gradient of the relevant function, e.g. the strength, thermal conductivity, ductility and the like, the intention being to increase the load-bearing capacity and efficiency of the material by avoiding abrupt changes in properties. Therefore, FGMs are intended to combine the positive properties of layer and single-piece composites in one material.
WO 98/53940 has disclosed a metal-ceramic gradient material, in particular for a heat shield or a gas turbine blade or vane. The metal-ceramic gradient material has a metallic base material, and also includes a ceramic and an additive for high-temperature oxidation resistance. In this case, the concentration of the metallic base material decreases from a metal-rich zone to a ceramic-rich zone, the concentration of the additive having a concentration gradient. Furthermore, WO 98/53940 has described a process for producing a metal-ceramic gradient material and a product produced therefrom, for example a gas turbine blade or vane or a heat-protection element of a gas turbine.